The Global Humanitarian Forum, chaired by former UN Secretary-General and Nobel Peace Laureate Kofi Annan, just released The Anatomy of a Crisis. The report concludes that more than 300 million people are already seriously impacted by climate change, and the annual economic cost is $125 billion per year.
By 2030, “worldwide deaths will reach almost 500,000 per year.” The total number of people affected will double, and costs will rise even more rapidly. The most devastating impacts will be felt in the poorest places on earth where there will be a need for vast increases in aid.
I would only add that these are, for the most part, the same places which have the most rapid population growth.